The present invention relates to the field of sludge disposal incinerators, and particularly to incinerators utilizing molten salts.
The handling of water-containing solids has long been a difficult problem, both from an engineering point of view and more particularly from an economics point of view. The burning or incineration of water-containing solids, hereinafter generically referred to as sludge, is an extremely fuel intensive operation. This is particularly the case for municipal and industrial sludges, which provide a large portion of the sludges which must be removed. The reasons that such burning or incineration is so fuel intensive include (1) the high heat of vaporization of water, (2) the low heat transfer through the water containing materials and (3) the difficulty, by conventional means, of creating small, low density, high surface area particles which are amenable to efficient heat treatment.
The outstanding need for more fuel-efficient means of treating sludge, as well as sludge treatment methods which avoid pollution of air or water, has lead to a proliferation of various techniques of treating sludge. Most industrial or municipal sludges are initially precipitated at a solids content of approximately 4% solid, 96% water. The resulting material may be dried mechanically by centrifuge, filter-press or vacuum belt filter to a resulting sludge of approximately 30% solid, 70% water. Even after this processing, the oxidation of the sludge is highly fuel intensive for the reasons noted above.
One technique for conditioning sludge for subsequent incineration is that of utilizing a jet mill or flash dryer. By the use of hot compressed air, the sludge can be dried to a dust-like consistency of approximately 80% solids, 20% water. This material is then in much better condition to be further oxidized or pyrolyzed. However, operation of a jet mill type device requires proper conditions for suspension of the water bearing solids within it, i.e., the sludge must be fluidized for travel through the mill. Consequently, the sludge must be introduced into the mill in as small pieces as possible, since large wet solids cannot be suspended in an airstream. Further, such mills require high pressure, and if the pressure falls below a threshold of about 2 inches of mercury, the sludge is not suspended in the compressed air. In such an event, reduction of the sludge to fine particles cannot occur. Further, the temperature of the air within the mill must be held at a high level so as to provide efficient heat exchange to remove water from the sludge. This means that the compressed air introduced into the mill must be heated to a very high temperature prior to introduction into the mill.
There remains a substantial need for an efficient means and method of treating relatively wet sludge which has not been elaborately preconditioned, and providing such treatment with maximum fuel efficiency.